Multi step switching, pertaining to the kind described above, are previously known in a number of various embodiments and the principal construction and the dimensioning rules concerning a none blocking three stage switching unit are shown and described in more detail in the publication "ISDN and Broadband ISDN" under the section 2:3 "Space-Division Switching" and specifically on page 33 with reference to FIG. 2.8.
The principal construction of a three stage switching unit is here described and dimensioned to be able to provide a none blocking signal transmission at a passage of incoming connections.
The structure of used first, second and third switching stages is not given in detail.
It is, nevertheless, known to form said switching stages so that these are adapted to pass used electrical information-carrying digitized signals, whereby electrical conductors are related to each other and structured according to the pattern indicated by the publication.
Taking the significant features of the present invention under consideration it can also be mentioned that it is previously known to be able to receive electrical information-carrying signals and to, through electro-optical converters, convert these to optical pulses of light and to transmit these light pulses on an optical conductor to an opto-electrical converter which receives said optical pulses and transmits corresponding electrical information-carrying signals.
Such optical information-carrying systems have been used within various electro technical applications, such as large switching units, in order to transmit information-carrying signals longer distances, as in between different or similar cubicles.
Taking the significant features, and thereto significant measures, of the present invention under further consideration it can be mentioned that totally optical switching units are previously known and described through the publication "Technical Digest of Conference on Optical Fiber Communication" in the article "Feasibility demonstration of 2,5 Gbit/s 16.times.16 ATM photonic switching matrix" on pages 93 to 94, by the authors D. Chiaroni et al and the publication "Proc. Topical Meeting on Optical Amplifiers and their Applications, postdeadline paper", 1992, in the article "Monolithically integrated 4.times.4 InGaAsP/InP laser amplifier gate switch arrays" on pages 38 to 42, by the authors M. Gustafsson et al.
In these referred publications it is described the usage of controllable optical switching components, such as optical switching matrixes, whereby optical light pulses, appearing on one of a number of available group related incoming optical conductors, can be selected and switched through a core to a, one of several available, selected outgoing optical conductor.
In order to simplify the understanding of the features if the present invention a reference to the publication "Proc. European Conference on Optical Communication", 1990, with the article "Characterization of a 1,5 m three-electrode DFB laser" on pages 279 to 282, by the authors R. J. S. Pedersen et al, can be made where it is described a tunable laser related transmitter.
A receiver in a laser related application is described in the publication "Proc. European Conference on Optical Communication", 1991, with the article "Performance of DBR active filters in 2.4 Gb/s systems" on pages 445 to 448, by the authors O. Sahlen et al.
The principles of said transmitter and receiver can be used within the present invention.
That which is shown and described in the following publication is also a part of the related art.
"Wavelength Conversion Laser Diodes Application to Wavelength-Division Photonic Cross-Connect Node with Multistage Configuration" H. Rokugawa et al. IEICE Trans. on Communication, Vol. E75-B, No. 4, April 1992, pages 267-274.
A three stage switching structure or unit is, through this publication, previously known with a principle construction that coincides with the basic conditions of the present invention.
It is here indicated (according to FIG. 1) the use of an opto-electrical signal converting stage (O/E), a stage intended to process electrical signals (ESP), an electro-optical signal converting stage (E/O), a switching stage adapted to optical signals (OSP), an opto-electrical signal converting stage (O/E), a stage intended to process electrical signals (ESP) and an electro-optical signal converting stage (E/O).
An connecting arrangement for the switching stage (OSP) is described in principal with reference to FIG. 2 which is specifically adapted to a wavelength separation, so that signals with different wavelengths can pass simultaneously through one single optical fiber and the conditions to increase the flexibility and capacity of such an optical communication network has thereby been created.
It can be specifically mentioned that the switching stages used here are dimensioned for one and the same capacity and that the optical switching stage (OSP) is dimensioned and adapted to the O/E- and E/O-stages.
The switching unit is thus dimensioned and adapted to a selected capacity and the possibilities to a gradual extension is neither indicated or mentioned.
It is further made clear, through that which is described in FIG. 2, that all outputs are connected to all inputs through the used optical stage.
It is besides this described possibilities to let a selected wavelength from every selected source (1.1-1.n) to an incoming block to be mixed before an optical signal with several wavelengths (.sub.1 -.sub.n) is transmitted through an outgoing block.
A separation of wavelengths is thus performed here to a number of possible receivers.
A requirement on an optical switching unit of this kind is that the selected light intensity of the information-carrying signals appearing on one of the inputs must be high enough to be sufficient to all the outputs.
A specially relevant prior art is found in the article "Trend of Photonic Switching Systems" S. Suzuki et al. IEICE, Trans. on Communication, Vol. E75-B, No. 4, April 1992, pages 235-242.
It is here described a number of switching units, intended to be able to transmit broadband signals.
The switching structure according to FIG. 15 can be regarded as being of a certain importance.
It is here described a switching equipment adapted to ATM-system using ATM-cells where the ATM-cells intended to pass through are connected or a multiplexing unit (MUX S/P) which restructure incoming parallel related ATM-cells to a serial related ATM-cell structure on one single conductor and these serial related ATM-cells can be stored within a memory.
Every ATM-cell, regardless of required bandwidth, is now to pass through the optical matrix connection OSM which requires a high speed, meaning that a speed corresponding to ATM-technology is here required through the complete connecting system.
A control of the OSM-stage is required so that, for every ATM-cell that is to pass through the OSM-stage, a selected input connection can be connected with a selected output connection.